Packaged and unpackaged semiconductor dice and other associated microcircuitry are widely used in the production of a variety of electronic devices. As the variety of uses continues to grow, a need has arisen in the industry for improvements in the technology relating to forming and packaging such electronic devices. In many cases, microcircuitry is mounted to rigid substrates such as printed circuit boards. Such substrates provide structural integrity to support the components mounted thereon and provide protection to the components from damage.
However, in many applications, electronic devices are required to have some flexibility, required to have continuous or periodic movement of the circuit as part of the end product function, required to accommodate odd configurations, or required to avoid breaking of the substrate upon impact with other objects. In such applications, microcircuitry in addition to electronic traces, are applied and/or mounted to flexible or polymer substrates. For example, and in no manner limiting to the present invention, different polymer based circuits are described in U.S. Pat. No. 5,448,110 entitled "Enclosed Transceiver" and assigned to Micron Communications, Inc.; U.S. Pat. Ser. No. 5,612,513 entitled "Article and Method of Manufacturing an Enclosed Electrical Circuit Using an Encapsulant" and assigned to Micron Communications, Inc.; U.S. Pat. No. 5,461,202 entitled "Flexible Wiring Board and Its Fabrication Method"; and U.S. Pat. No. 4,317,011 entitled "Membrane Touch Switch."
In many polymer based circuits, such as some of those described above, an encapsulant is utilized over the entire circuit as opposed to just the individual components. In other polymer based circuits, only individual components mounted on polymer or flexible substrates are encapsulated to allow for an electronic device that is relatively more flexible than when the entire circuit is encapsulated. Further, in other polymer based circuits, encapsulant or other coating materials may be used as spacers to configure devices such as membrane touch switches. However, in all of these different polymer based circuits, the adherence of the encapsulant or coating material to the polymer film or flexible substrate is of substantial importance to the method of producing such circuits and the resulting electronic devices.
Several methods of promoting adhesion of coatings and adhesives, including encapsulant, to polymer films are currently in use. Primarily such methods include mechanical abrasion, flame, corona, and chemical primering by either direct mechanical or chemical attack of a surface of the polymer film or by coating the surface of the polymer film with another adhesion promoting coating material. For example, an adhesion promoting resin such as Chemlok Primer AP-133 supplied by Lord Corporation, Erie, Pennsylvania, is currently utilized. Other chemically print treated polymer films, such as certain Melinex.RTM. polyester films, are available from Imperial Chemical Industries or ICI Americas Inc., having a place of business in Wilmington, Del.
However, such adhesion promoting methods, like flame, corona, mechanical abrasion, and chemical primering, require substantial capital investment and, in many cases, is cost prohibitive. Further, some print treated polyester films, like that available from ICI Americas Inc., are ineffective as adhesion promoting surfaces for adhesion of certain encapsulants. Therefore, there is a need in the art for making polymer based circuits with improved adhesion promoting methods. Such methods would improve upon the structural integrity and the reliability of polymer based circuits.